The first thing you notice is the attention to detail, the physics of the environment around you looks amazing, how leaves flow with the wind, how your vision gets blurred by mud, the beautiful landscape and the lighting effects. However looking good isn't the only thing Metro does, but the combat system is easy to get used too, the aim and response is quick and smooth making it easier to eliminate multiple targets. You will always be on your toes as the game always tests your readiness to a surprise attack, the ability to sense the enemies location by sound helps a lot since the audio is well calibrated to enemies position. The game tutorial is quick and simple as are the controls, anyone who has played a FPS would easily figure out what to click and what to do and it also does a good job explaining it to new gamers.
However there are some points that stops you from really get into this game fully, there isn't that much diversity in weapons. The game is very short and you wind up ending it and wanting more. The currency used is high grade military ammo which can also be used in your weapons to deliver higher damage. The customization system seems redundant, enemies drop weapons that are already customized and buying those customizations seems to be a waste of needed ammo, of course buying these upgrades are optional but a better use would have been to increase states of a weapon for example it's damage, fire rate, etc instead of adding a scope which you could have found easily dropped by the weakest of enemies.
I would strongly recommend playing Metro 2033 before playing this game as the story is a continuation to what you did before. Last Light tries to explain it to new gamers however you will have more understanding of what is going on if you played the previous installment.
All and all its a very nice game which I strongly recommend playing.